The present invention generally relates to a combustion burner and, more particularly, to a combustion burner assembly of a type wherein heat of exhaust gases to be discharged is used to preheat both combustion air and gaseous fuel.
A burner assembly is well known wherein the pressure of the gaseous fuel and that of the combustion air are equalized to each other by means of an equalizing valve.
On the other hand, for the purpose of saving energy, it is a recent trend to use the combustion air after it has been preheated by heat recovered from exhaust gases.
However, in the prior art burner assembly employing the pressure equalizing control, it has been found that, when the combustion air is preheated, the combustion air expands which causes an increase in pressure which in turn brings about an increase in pressure of the gaseous fuel. The consequence is that the air-fuel ratio changes substantially, resulting in the emission of soot with a lowered combustion efficiency.
In view of the foregoing, where the pressures of the combustion air and the gaseous fuel are controlled to equalize with each other, the prior art burner assembly has a problem in that it requires the use of specially designed, expensive compensating equipment for each of the gaseous fuel supply line and the combustion air supply line to compensate for the change in air-fuel ratio.